Laser pulse formation can be achieved using mode locking or Q-switching. For example, external-cavity laser diodes can use a diffraction grating to modify the output wave front and to mode-lock the diode. On the other hand, a Q-switched laser can use a variable attenuator to initially reduce the Q-factor (quality factor) of the laser optical resonator, thereby increasing population inversion, and the attenuator is subsequently “switched” to achieve a high Q-factor, thereby producing a Q-switched pulse. An external seed laser beam can be used to modulate the Q-switched laser output.